1. Field of the Invention
The present invention relates to a cesium-lithium-borate crystal and crystals with substituted chemical compositions thereof. More particularly, the present invention relates to a cesium-lithium-borate crystal and crystals with substituted chemical compositions thereof which are used as frequency converting nonlinear optical crystals in laser oscillators and optical parametric oscillators used in blue and ultraviolet lithography, laser microprocessing, scientific and industrial measurement and laser nuclear fusion, a method for manufacturing same, and an optical apparatus using same.
2. Prior Art and Problems
Laser oscillators used in ultraviolet lithography, laser microprocessing, scientific and industrial measurement and laser nuclear fusion must generate stable blue and ultraviolet rays efficiently. One of the methods to achieve the above object which is attracting the general attention to day is the method to efficiently obtain blue and ultraviolet rays by frequency conversion of a light source using nonlinear optical crystals.
A pulse YAG laser oscillator, a type of laser oscillators, for example, uses nonlinear optical crystals to convert frequency of a light source to generate the third (wavelength: 355 nm) or the fourth (wavelength: 266 nm) harmonics of the pulse YAG laser.
Many contrivances on the frequency converting none linear optical crystals which are indispensable for generating ultraviolet rays have been announced. For example, beta barium methaborate (.beta.-BaB.sub.2 O.sub.4), lithium triborate (LiB.sub.3 O.sub.5), cesium triborate (CsB.sub.3 O.sub.5) and other borate crystals are known. These frequency converting nonlinear optical crystals for generating blue and ultraviolet rays will pass wavelengths of 200 nm and below, and have a large nonlinear optical coefficient.
It is very difficult, however, to grow crystals of .beta.-BaB.sub.2 O.sub.4, one of such frequency converting nonlinear optinal crystals, because of the tendency of causing phase transition in the production process. Further, angular allowance is very tight, and thus this particular substance has a very low level of generality.
Furthermore, for LiB.sub.3 O.sub.5 other frequency converting nonlinear optical crystal, the growth time is very long as a result of flux growth in the production process, and this crystal is only good for phase matching for rays down to about 555 nm wavelengths for second harmonic generation. This crystal is used, for example, for generation of the third harmonic (wavelength: 355 nm) of Nd-YAG lasers, but cannot be used for generating the fourth harmonic (wavelength: 266 nm)